The typical internal combustion engine is cooled by providing a coolant (oftentimes called anti-freeze) in cavities that surround the engine. A typical coolant is an aqueous glycol composition such as aqueous ethylene glycol or propylene glycol. These glycols function to reduce the freezing point of coolant and raise the coolant's boiling point, thus assuring that the vehicle's coolant will not freeze or boil over. During operation of the engine, air is constantly drawn into and expelled from the coolant composition. When the coolant is heated during engine operation, air is expelled from the coolant. When the engine is at rest and the temperature of the coolant drops, air is absorbed by the coolant up to the saturation point. This repeated cycle in the life of a coolant provides an oxidation mechanism by which metal ions that are generated by corrosive attack of engine surfaces are subjected to instantaneous oxidation and glycol is thermally oxidized.
Essentially all metal ions when converted to their highest oxidation state form insoluble hydroxides and oxides in the coolant composition, thus forming a precipitate that collects within the engine's coolant chamber. Some of the metals are oxidized to form precipitated hydroxides that deposit on the wall of the coolant chamber and interreact by condensation reactions to form a beneficial oxide layer. This layer protects the engine block from serious corrosion. It would be undesirable to have present in the coolant a component that attacks that beneficial oxide layer and causes its removal. Such action eventually leads to serious corrosion of the engine block. One such component that would attack the beneficial coating if present in the coolant in deleterious amounts, is the chloride ion. It will convert the oxides into soluble chlorides, thus wiping away the beneficial oxide layer. For example, it will convert iron oxides through thermally induced chlorination, to ferric and ferrous chlorides, and aluminum oxides through thermally induced chlorination, to aluminum chloride. These chlorides are very acidic and notorious Friedel-Craft catalysts. They can accelerate the decomposition of the coolant and cause corrosion of metal surfaces.
Other of the precipitates form within the coolant and serve no useful function. Most of these precipitates are of sufficient size so as to deposit from the coolant to the bottom of the coolant chamber. A minor portion, more like a trace amount, of the precipitates have such a small size (more like microscopic in size) that they remain dispersed in the coolant. Eventually these precipitates have to be removed and thus flushing of the coolant system is an appropriate procedure.
The trace amounts of these metal hydroxides that remain suspended particulates within the coolant will, with time, chemically interreact to form dimeric and oligomeric condensates. Such condensates remain suspended (dispersed) in the coolant. These condensates are difficult to remove by filtration because they have an extremely small particle size. Because the metal atoms in these condensates are at their maximum state of oxidation, further oxidation of the coolant will not cause these condensates to be further oxidized. Nor will further oxidation cause these condensates to drop out of dispersion in the coolant.
As noted above, some of the coolant becomes chemically altered. For example, a minor portion of the ethylene glycol is periodically thermally oxidatively attacked to form a number of decomposition products such as glycolic acid, formic acid and oxalic acid. These acids per se do not cause the coolant to become acidic, that is, cause the coolant to have a pH below about 7. As pointed out in an article by Cooper, Hannigan and McCourt, "A One Thousand Car Assessment of the U.S. Car Population Cooling Systems," SAE Technical Paper Series, Proceedings of the 2nd Automotive Corrosion Prevention Conference, Automotive Corrosion and Prevention Conference, Dearborn, Mich., Dec. 5-7, 1983, the mean pH of the ethylene glycol coolant in the car population is 8.7, with only 2.3 percent of the cars having coolant with a pH of 7 or less. Since the pH of the coolant is dictated by the buffer system in the coolant, the coolant will generally possess a substantial alkali metal ion content. This causes the acids to compete with the acidic component of the buffer for the alkali metal ions. These decomposition products, as salts and free acids, remain as soluble components of the coolant. Because they are acids, their accumulation in the coolant reduces the coolant's pH. With reduction of pH comes increased corrosion of engine surfaces resulting in increased concentrations of metal hydroxide and oxide precipitates. Eventually, the coolant becomes so fouled by this decomposition that it must be either replaced or reconditioned.
Conley, J. H. and Jamison, R. G., "Reclaiming Used Antifreeze," MERADCOM Report 2168, U.S. Army MERADCOM, Fort Belvoir, Va., March 1976, describe an early effort by the U.S. Army in treating recycled vehicle coolant. As these authors note, coolants are repeatedly subjected to oxygenation. Such oxygenation is the cause for thermal oxidative degradation of the coolant. The authors recommend discarding coolant with a freeze point above 5.degree. F., which means that the coolant is too degraded for further treatment. A coolant with such a high freeze point would have a low pH because of thermal oxidation of the ethylene glycol. The authors proposed two methods. Method I involves
1. Take freeze point of coolant. If above +5.degree. F., discard; do not retain for processing.
2. Place antifreeze drained from vehicles into holding tank.
3. Allow antifreeze to settle for several hours or until fairly clear. The longer the settling time, the more solids will have settled and less will remain to be filtered.
4. Filter through a cloth filter.
5. Pass filtrate through cationic resin (IR-120 or equivalent).
6. Pass effluent through activated carbon.
7. Pass effluent through calcium carbonate (marble).
8. Add inhibitor which involves bringing the antifreeze to its normal range of reserve alkalinity and pH with Federal Specification 0-I-490 corrosion inhibitor. Check freeze point, adding new antifreeze or water to obtain desired freeze point.
9. Flush vehicle cooling system with water and recharge.
Method II proposed by the authors involves
1. Take freeze point of coolant. If above +5.degree. F., discard; do not retain for processing.
2. Drain cooling system, and filter the antifreeze through cotton batting or cloth filter to remove rust and solids.
3. Add Inhibitor A at the rate of 3 percent, or 1 pint per 16 quarts coolant.
4. Flush cooling system with water until the water is clear.
5. Replace the inhibited, used antifreeze solution.
Method I described by Conley and Jamison above, with the exception of the use of cation exchange resin, activated carbon and calcium carbonate, was employed with minor differences by PECO (formerly Philadelphia Electric Co., Philadelphia, Pa.) in 1987 to successfully reclaim antifreeze.
There are described in the literature a variety of systems directed to the treatment of spent engine coolant that allows for the recovery and refurbishing of such coolant. Illustrative of such technology are a series of patents to the Wynn Oil Company, such as U.S. Pat. Nos. 4,083,393, 4,091,865, 4,109,703, 4,178,134, 4,209,063, 4,293,031, 4,791,890, 4,793,403, 4,809,769, 4,899,807, 4,901,786, 5,201,152, 5,078,866, 5,306,430, 5,318,700, and Re.31,274. For example, Filowitz, et al., U.S. Pat. Nos. 5,021,152 and 5,078,866 relate to the treatment of coolant with agents that precipitate anions and cations and the removal of such precipitants. The patents describe the addition of "Composition A" and "Composition B" to the recycled coolant. According to the patents, "A" precipitates anions, i.e., the negatively charged ion, especially the ion that migrates to an anode in electrolysis, such as sulfate, chloride, etc. "B" precipitates cations, such as metal ions--i.e. of lead, iron, copper, etc. According to the patents, Composition A is a material called "Protazyme," which is defined as an 8% aqueous solution of cationic polyelectrolyte HYDROFLOC 865 having the chemical formula ##STR1## where X is undefined. The patents confuse the description of Composition B. Composition B, called "NETAMOX," is "a 5% aqueous solution of anionic polyelectrolyte, or equivalent, and a 5% aqueous solution of heavy metal precipitant" that appear to be "Sodium dimethyl dithiocarbamate in 0.5% to 1.5% aqueous solution form" and "HYROFLOC 495L" that possesses the chemical formula ##STR2## where X is undefined. In chemistry, the "X" group is frequently used to denote halogen.
It should be noted that the formula of HYDROFLOC 865 and 495L is the same for materials possessing entirely different properties. If Composition B is 5% of the anionic polyelectrolyte and 5% of the DTC solution, what is the rest of the composition? That is not explained in the patents.
In both patents, a filtered coolant is treated by the addition of chemical agents such as corrosion inhibitors, pH adjustment chemicals and fresh coolant, such as ethylene glycol or propylene glycol, depending upon the base of the spent coolant being treated.
PCT/US92/00555 and U.S. Pat. No. 4,946,595, to Miller, describe a process for the treatment of a spent coolant outside of the engine. The treatment involves an oxidation step, which, as noted above, will have no impact on the character and properties of the spent coolant. Another step utilized by Miller is the treatment of the spent coolant with an alkali such as sodium hydroxide, to not only raise the pH, but to also form salts of the coolant decomposition products, such as glycolic acid, formic acid and oxalic acid. According to Miller, these salts precipitate from the coolant. Interestingly, Miller also describes adding such salts to the coolant to create a common ion effect. In the latter case, Miller is suggesting that the so-called salts that precipitate are soluble in the coolant, clearly indicating that salt formation does not result in acid removal by precipitation. The next step in the process is to pass the coolant through a series of filters, the first filter effecting a coarse separation, and the second filter effecting a finer separation. An optional treatment is to pass the treated coolant through an ion exchange resin to remove alkaline earth metal ions. However, at the pH of the coolant at that step of the process, all such alkaline earth metal ions are fully oxidized to their hydroxides which are insoluble in the coolant. All but a trace amount of these hydroxides would have already precipitated from the coolant.
The PCT application describes a variety of additive packages for spent coolant. For example, the PCT application (at page 15) describes the use of sodium dimethyldithiocarbamate as part of an inhibitor package in the following terms:
At page 20, in Table F of the PCT application, Miller describes a chemical additive package that contains sodium dimethyl or diethyl dithiocarbamate. The following table embellishes on the formulation described in Table F by functionally describing the components where such makes sense to do: